1. Field of the Invention
Applicant's invention relates to an apparatus and method to remove fines or small particles from the liquid and particulate mixture used in fracturing or gravel packing a subterranean well.
2. Background Information
Gravel packing a subterranean well addresses the problem encountered by many oil and gas producers; namely, sand flow into the well bore from unconsolidated formations. Sand flow can gradually fill the well bore until production perforations are covered, resulting in decreased production, if not total loss of production. Sand flow also damages equipment. Gravel packing eliminates, or at least reduces to trace amounts, sand flow from unconsolidated formations by placing a filtering system within the well and formation.
The concept of gravel packing is fairly simple. A screen of a pre-selected size is placed inside the well casing adjacent to the producing formation. If well casing is not used, a screen of pre-selected size is hung from the well bore adjacent to the producing formation. A mixture of a premeasured gravel packing particulates and a carrier liquid, such as water or material of similar density, is forced down the well bore under sufficient pressure and volume to deposit the gravel packing particulates against the face of the producing formation and the screen. Thus, creating an avenue through which the oil or gas being produced may travel without interruption to the well bore. The gravel packing particulates used are sized by the oil and gas industry as 20-40, 40-60, etc., grain size (U.S. Sieve) in inches of grain diameter. For example, a 20-40 grain size mixture (U.S. Sieve) contains grain sizes of 0.031" to 0.0165".
In conventional day gravel packing procedures, extreme care is used to initially choose the proper size of gravel packing particulates, and to assure that the particulates are not damaged before use; for example, during shipment to the well site or while being fed into the mixer. Yet, even though the particles are chosen for their size and carefully placed in the mixer, these same particles are forced under at least 50 psi of pressure out of the mixer and at least 1,500 psi of pressure from a high pressure, high volume pump into the well bore. In effecting this type of pressure, the opening and closing of the inlet and outlet valves of the mixer and pump crush some of the gravel packing particulates, producing fines (smaller particles) which clog the avenues created by the undamaged gravel packing particulates, and in turn cause production to decrease.
Fines are also created during the fracturing process. Generally, fracturing is another method used to increase production. Fracturing a well is accomplished by forcing a liquid and particulate mixture down the well bore to open up a new production zone. Just as in gravel packing, the particulates are chosen for their size and shape. Yet, mixers and high pressure, high volume pumps are also used in the fracturing process. Thus, fines are again created by the opening and closing of the inlet and outlet valves of the pump and mixer. Consequently, just as in gravel packing, the avenues created by the fracturing process are also clogged by fines which in turn reduce production. Therefore a need exists for a method and apparatus for removing fines that are created by the inlet and outlet valves of the mixer, pump and other equipment that the particulates come in contact with during the gravel packing or fracturing processes.